SELECT [Assignment work by day].ProjectName, [Assignment work by day].ResourceName, [Assignment work by day].TaskName, [Assignment work by day].TimeByDay, [Assignment work by day].AssignmentWork, [Assignment work by day].AssignmentActualWork, [Timesheet 2013].ActualWorkBillable, [Timesheet 2013].ActualOvertimeWorkBillable, [Assignment work by day].Resource_Manager, [Assignment work by day].Group_Manager
FROM [Assignment work by day]
LEFT JOIN [Timesheet 2013] ON ([Assignment work by day].ResourceName = [Timesheet 2013].ResourceName) AND ([Assignment work by day].TimeByDay = [Timesheet 2013].TimeByDay) AND ([Assignment work by day].TaskName = [Timesheet 2013].TaskName) AND ([Assignment work by day].ProjectName = [Timesheet 2013].ProjectName);

Last edited by ZiadZ; May 2nd, 2013 at 11:36 AM.
Reason: Problem Solved!

SELECT [Assignment work by day].ProjectName
, [Assignment work by day].ResourceName
, [Assignment work by day].TaskName
, [Assignment work by day].TimeByDay
, [Assignment work by day].AssignmentWork
, [Assignment work by day].AssignmentActualWork
, [Timesheet 2013].ActualWorkBillable
, [Timesheet 2013].ActualOvertimeWorkBillable
, [Assignment work by day].Resource_Manager
, [Assignment work by day].Group_Manager
FROM (
-- assignment query goes here
) AS [Assignment work by day]
LEFT OUTER
JOIN (
-- timesheet query goes here
) AS [Timesheet 2013]
ON [Timesheet 2013].ResourceName = [Assignment work by day].ResourceName
AND [Timesheet 2013].TimeByDay = [Assignment work by day].TimeByDay
AND [Timesheet 2013].TaskName = [Assignment work by day].TaskName
AND [Timesheet 2013].ProjectName = [Assignment work by day].ProjectName

Thank you for the fast reply!
I'm getting the following errors :
Incorrect syntax near the keyword 'AS'.
Incorrect syntax near 'MSP_EpmProject'.
Incorrect syntax near 'MSP_EpmAssignmentByDay'.
Incorrect syntax near ','.